The present invention relates to structural cables used in construction works. It applies, in particular, to the anchoring of stay cables or pre-stressing cables.
Such structural cables are frequently made of a plurality of parallel tendons. Their ends are anchored using blocks in which channels are formed for receiving and blocking individually the tendons, for example by means of split conical jaws.
The tendons of the cable are made of metal, for example in the form of strands. In the main part of the cable, they are often contained in individual sheaths of plastic material which isolate them from the environment and thus protect them from corrosive agents. In order to firmly hold a tendon in the anchor block, its plastic sheath is removed in the anchoring region. It is then necessary to provide particular anti-corrosion protection measures in the anchoring region. In general, the volume containing the exposed portions of the tendons is filled with a protective material injected under pressure into the anchoring region.
The injection step must be carried out with caution so as to avoid any remaining voids in the volume to be filled, since such voids may be the starting point of the corrosion phenomenon for the metal of the tendons, in particular if water leaks in.
Wax is an interesting example of protective material to be injected in the anchoring region, in view of its properties of adherence, corrosion protection and fatigue behavior. The wax is in a solid state at room temperature and becomes liquid when heated. It can thus form a reversible filling, which is useful for allowing inspection of the anchorage.
Other injectable protective materials can be used, in particular thick materials, e.g. grease, or hardening materials, e.g. a resin or a polymer.
For a given construction work, the protective material is selected by taking into account the required functionalities for installing and or maintaining the anchorage.
The volume to be filled with protective material includes a chamber located on the front side of the anchorage and closed by a cover. The end portions of the tendons of the cable, protruding from the anchorage, are located in that chamber.
In certain anchorage designs (see, e.g., WO 01/20098 A1), there is a second chamber at the rear of the anchor block, in which the ends of the individual sheaths of the tendons are located. The rear face of that second chamber is closed by a sealing device, of the stuffing box type or the like, through which the sheathed parts of the tendons extend. The filling of the second chamber with the protective material can be carried out separately from the filling of the first chamber located on the front side of the anchorage, or simultaneously. In the latter case, one or more communication channels are generally provided through the anchor block, in addition to the channels containing the tendons, to allow the injected material to flow.
In other kinds of anchorage design (see, e.g., EP 0 896 108 A2 or EP 1 227 200 A1), the rear side of the anchor block does not have a second chamber containing the tendons collectively. The ends of the individual sheaths of the tendons are located in the channels of the anchor block, or in extensions of those channels provided on the rear side of the anchor block.
The injection is performed once the tendons have been installed and tensioned. Conventionally, the filling material is injected by an inlet located in a low portion of the anchorage until it flows out by a vent located in a high portion of the anchorage. This minimizes the risk of leaving voids in the volume to be filled.
However, that risk is not completely eliminated. When the level of the filling material rises and reaches the anchor block, the different channels form competing flow paths. The head loss in those channels is not uniform because the contents of channels can be different from one channel to another. For example, if the block has one or more communication channels in addition to the channels containing tendons, the fluid material has a tendency to flow through the communication channels, so that the other channels may remain with voids, thus exposing the metallic tendons. The possible presence of debris in a channel when the injection starts also changes the head loss through that channel and causes a risk of incomplete filling. If there are no communication channels and/or if there is a chamber only on the front side of the anchorage, it is also quite difficult to ensure a complete filling of the channels containing the tendons.
There is thus a need for an improved method of filling the inner volumes of an anchorage system to protect the tendons and other metallic components of the anchorage from corrosion.